Generally, as the body thickness of a scanned part increases, the output value of an X-ray detector decreases and its error increases. For this reason, noise of an X-ray CT image reconstructed for a region with a large body thickness increases. On the other hand, in a conventional X-ray CT apparatus, an X-ray CT image of an object has usually been generated using one reconstruction filter in each CT scan. For this reason, there have been cases in which an optimal X-ray CT image can be provided for a certain part of the object but the optimal image quality is not obtained for other regions.
In such a case, there is known an X-ray CT apparatus that outputs an X-ray CT image, in which a plurality of reconstructed images are combined by calculating a plurality of reconstructed images through superimposing a plurality of reconstruction filters, such as a smoothing filter and a sharpening filter, and setting an addition coefficient corresponding to the CT value at each point for each of the reconstructed images and adding the addition coefficients (PTL 1).